Pressure-sensitive adhesives (PSAs) are known to possess properties including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be removed cleanly from the adherend. Materials that have been found to function well as PSAs include polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power. PSAs are characterized by being normally tacky at room temperature (e.g., 20° C.). PSAs do not embrace compositions merely because they are sticky or adhere to a surface.
U.S. Pat. No. Re. 24,906 (Ulrich) discloses a pressure-sensitive adhesive tape, the adhesive layer of which comprises a copolymer of acrylic acid ester and a copolymerizable monomer such as acrylic acid, described therein as an “acrylic pressure-sensitive adhesive tape”. Although acrylic pressure-sensitive adhesive tape may provide acceptable strength and good adhesion, there has been a need for even higher shear strength, especially at elevated temperatures, without any reduction in adhesion, particularly in peel strength.